Hybrids of Aluminum Hypophosphite and Ammonium Polyphosphate: Highly Effective Flame Retardant System for Unsaturated Polyester Resin

摘要

A novel flame-retardant unsaturated polyester (UP) was obtained by introducing ammonium polyphosphate (APP) and aluminum hypophosphite (AHP) into UP matrix. The UP/APP/AHP composites obtained were characterized by Fourier Transform Infrared Spectra (FTIR). From limiting oxygen index (LOI), microscale combustion calorimetry (MCC), and UL-94 tests, the UP/APP/AHP composites present significantly enhanced flame retardancy when compared to pure UP, such as passed UL-94 V-0 classification, decreased peak heat release rate (PHRR) maximally by 50.0% and total heat release (THR) maximally by 22.0%, and increased LOI by 34.8%. Thermal degradation behaviors of composites studied by thermogravimetric analysis (TGA) suggest that APP/AHP hybrids have a higher catalytic charring efficiency than APP alone. Char morphology investigated by scanning electron microscopy (SEM) indicates that the UP/APP/AHP composites form a compact and intumescent char on the sample surface during combustion, which could retard the transfer of heat and oxygen. Thermogravimetric analysis/infrared spectrometry (TGIR) results reveal that the APP/AHP hybrids reduce the release amount of combustible gas from polymer matrix during combustion. The UP/APP/AHP system acts in gas phase through flame inhibition and in condensed phase through charring, resulting in significantly enhanced flame retardancy. This work combining condensed-phase mechanisms with gas-phase mechanisms in flame retardance of UP would stimulate more efforts to explore highly effective flame-retardant system of polymers. (C) 2016 Society of Plastics Engineers